1. Field of the Invention
The present invention relates to a magnetic material adapted for use in a transformer, a coil or the like, and more particularly to a magnetic oxide material of a low magnetic loss employing a Ni type ferrite material as a main raw material or ingredient, and a method for making same.
2. Prior Art
Ferrite materials of Mn type (Mnxe2x80x94Zn) or Ni type (Nixe2x80x94Zn) are known as a core material for a transformer or a coil or the like, but the ferrite material of Mn type has been principally employed. This is because the Mn type ferrite material has a smaller magnetic loss and higher magnetic characteristics in comparison with the Ni type ferrite material. A core of the Mn type ferrite can provide a coil component of a high efficiency.
With the recent significant compactization (or, size reduction) and weight reduction of electronic devices, it is strongly desired, also in such coil component, to be a module which integrates an electronic circuit including a coil as a functional component, and which can be incorporated in another electronic devices (for example an ultra small DC-DC converter, an ultra small inductor, etc.)
However, the Mn type ferrite material, which has been used in the past, though having a low loss and high magnetic characteristics, does not allow direct coil winding on the core because of a low electric resistance, so that the coil has to be formed so as to wind on a bobbin or an insulation sheet, and this fact has been an obstacle to compactization of the coil component. On the other hand, the known ferrite material of Ni type allows direct coil winding on the core because of a higher electrical resistance in comparison with the Mn type and is advantageous for compactization, but the magnetic loss is excessively high for practical use.
The present invention has been made in consideration of the drawbacks in the related art, and is to provide a Ni type ferrite material of a low magnetic loss.
More specifically, a magnetic oxide material according to a first aspect of the present invention is characterized by being formed by adding MnO2 in an amount of 0.1 to 1 mol % to a ferrite raw material of a composition containing Fe2O3 in 40 to 50 mol %, ZnO in 20 to 33 mol % and CuO in 2 to 10 mol % and NiO in the remainder.
In a preferred embodiment of the present invention, in the above-mentioned magnetic oxide material, MnO2 is preferably added after a calcination of the ferrite raw material.
In another embodiment of the present invention, the above-mentioned magnetic oxide material preferably has a lattice constant of 8.4090 to 8.4105 xc3x85.
Also in another embodiment of the present invention, the above-mentioned magnetic oxide material preferably has a coercive force at the room temperature of 16 xcexcm or lower and a coercive force at 80xc2x0 C. of 4 A/m or lower.
In still another embodiment of the present invention, the above-mentioned magnetic oxide material preferably has a sintered density of 5.15 to 5.20 g/cc.
Also in still another embodiment of the present invention, the above-mentioned magnetic oxide material is characterized in having a Curie temperature of 130 to 150xc2x0 C.
Also in still another embodiment of the present invention, the above-mentioned magnetic oxide material preferably has a particle size of MnO2 of 100 xcexcm or less.
In the aforementioned range of composition, there can be obtained a Ni type ferrite material of a low magnetic loss. This is estimated because an addition of MnO2 to the mother powder reduces a lattice strain in the ferrite crystal with an increase in the content of MnO2, thereby reducing the coercive force and decreasing the hysteresis loss.